My feedback on 37’s and MPG

[phatboy64]

I am not sure where the best place to post this so I am posting it here.

I took my 2023 3500 limited HO SRW on its first long trip (800 miles) since lifting and putting 37x12.5x20’s on it. I was carrying about 500 lbs in the bed. My wife and two dogs in the cab. The trip was mostly highway at 10 mph over speed limit so 75 and 80 mph. There was two detours that took me on some roads and idle time at a few rest areas. Hand calculated I got 17.9 mpg, interestingly enough the the dash cluster registered 17.8 mpg ( I reset it right before leaving my driveway). I guess my point is I am very happy with the mileage I am getting with the 37’s, when reaching putting 37’s on I read conflicting informations regarding how much they would affect mileage. FWIW MPG is not really a concern of mine but I thought others may find this information helpful.

 

[UglyViking]

That MPG isn't bad at all for a HO truck. I don't know what lift, and tires you've got (AT vs MT makes a difference slightly), and assume you've got the 3.73 gearing, so that's solid. My truck got mid-high 19s when I was driving 95N for almost 16 hours. I think if I would have gone a more leisurely pace I could have gotten it up towards 20-21.

 

[tchur1]

Im on 37s but not lifted and see very similar MPGs on my evic. Have you corrected your speedo for tire size?

 

[thecastle]

Hu, I have a 2019 Stock 3500 HO with the factory 20" rims. At 70-80 mph on the hwy and a few blasts to 90-100 passing on the right those who are impeding traffic on the left. I get an indicated 17.5mpg and 16.4 by measuring it at the pump. Barn door aerodynamics. But I never get better than about 16-17 indicated in around town driving, and usually 12-13 in town. 8-9 while towing. At low speeds like under 60, I can breifly see 18-22mpg, but not as an average.

 

[phatboy64]

That MPG isn't bad at all for a HO truck. I don't know what lift, and tires you've got (AT vs MT makes a difference slightly), and assume you've got the 3.73 gearing, so that's solid. My truck got mid-high 19s when I was driving 95N for almost 16 hours. I think if I would have gone a more leisurely pace I could have gotten it up towards 20-21.

Yeah, I spent most of my time heading out of Ma on I84 then I81 all the way down to I77 to Charlotte.
I have a Carli 3.25 backcountry lift with the add a pack. Tires are Wildpeek AT3s and stock 3.73s. Pretty happy all in all. Truck ran so smooth, there were times I hit 90 without realizing it…ACC came in handy at times. No regrets with the 37s

 

[phatboy64]

Im on 37s but not lifted and see very similar MPGs on my evic. Have you corrected your speedo for tire size?

I did but due to a few reasons it is not 100%, at the speeds I was driving I was 4 mph off according to Waze

 

[phatboy64]

Hu, I have a 2019 Stock 3500 HO with the factory 20" rims. At 70-80 mph on the hwy and a few blasts to 90-100 passing on the right those who are impeding traffic on the left. I get an indicated 17.5mpg and 16.4 by measuring it at the pump. Barn door aerodynamics. But I never get better than about 16-17 indicated in around town driving, and usually 12-13 in town. 8-9 while towing. At low speeds like under 60, I can breifly see 18-22mpg, but not as an average.

I really haven’t measured my around town MPG but if I believe my dash cluster it is around 15 mpg…

 

[AH64ID]

I did but due to a few reasons it is not 100%, at the speeds I was driving I was 4 mph off according to Waze

4 mph fast or slow? At what speed? That will have an effect on hand calc’d mileage.

 

[tchur1]

4 mph fast or slow? At what speed? That will have an effect on hand calc’d mileage.

This is exactly why I bring it up. I haven’t corrected my Speedo for 37s yet and my evic shows 17.4 average right now. So I’m likely doing a bit better than that in reality.

 

[phatboy64]

4 mph fast or slow? At what speed? That will have an effect on hand calc’d mileage.

The speedometer was 4 mph slower. So if waze said I was going 79 my speedometer said 75.

 

[phatboy64]

So if I have my math right in the example below (those are not my actual numbers)

8 hours at 79 mph = 632. 632/27 gallons = 23.40
8 hours at 75 mph = 600. 600/27 gallons = 22.22

That is a 1.19 mpg less however that assumes one would have to drive that speed the whole time. Using fuzzy math I would would say split that in half and call it .6 mpg difference. But then again the only real way to get a real average mpg for that would be to take that same trip more then once and average the average…

 

[AH64ID]

The speedometer was 4 mph slower. So if waze said I was going 79 my speedometer said 75.

That’s a 5% speedo error, meaning you got 5% better mileage than hand calc’d. Seems crazy high for the unsprung weight and added drag if the lift.

 

[phatboy64]

So yeah. I am very happy. Like I mentioned MPG was low on my list of concerns when making the decision to to move up to 37's, Ride quality was on the top.
I feel I got a win on on both.
My advice to anyone who on the fence about moving to 37's .... go for it.

 

[UglyViking]

That’s a 5% speedo error, meaning you got 5% better mileage than hand calc’d. Seems crazy high for the unsprung weight and added drag if the lift.

Idk about his specific setup, but I've found my mpg calc to be within .5mpg across the board (more or less). Even if you call it a full mpg, I've never gotten below 17mpg around town driving on summer fuel. 2.75"/1" thuren coils and 37x17 at tires.

Maybe others fuel is different, or elevation differences, or driving styles, or the definition of "city/around town", etc. Idk.

Perhaps I should start hand calving for longer durations and see if I experience any real differences now that the engine is broken in and the cp3 is in.

 

[BilletWilson]

Im gearing up to run 37's and have been debating installing 4.10s when I do. How do you feel the stock 3.73's are doing?

 

[UglyViking]

I can only speak for myself, but I feel that 3.73s are fine. Are they ideal? No. I'm planning to do gears when I do lockers personally, but if I was mostly on road, and now towing heavy often, I'd have no issues with keeping the 3.73s.

 

[phatboy64]

I agree. 3.73s are fine. Sometimes driving around town on secondary roads and getting stuck behind someone @ around 25 mph I feel like I could use a few more RPMs.
Primary roads and highway are no issue at all.

That said if I was towing heavy I think I would bump up to 4.10s.

 

[AH64ID]

Idk about his specific setup, but I've found my mpg calc to be within .5mpg across the board (more or less). Even if you call it a full mpg, I've never gotten below 17mpg around town driving on summer fuel. 2.75"/1" thuren coils and 37x17 at tires.

Maybe others fuel is different, or elevation differences, or driving styles, or the definition of "city/around town", etc. Idk.

Perhaps I should start hand calving for longer durations and see if I experience any real differences now that the engine is broken in and the cp3 is in.

In the nearly 15K miles I've put on my 2022 I've averaged 8.2% error on the EVIC, but as high as 22.6% (3.7 mpg optimistic) and as low as -.06% (.2 mpg pessimistic). The 8.2% error translates to ~1.1 mpg optimistic as an average. I subtract 10% while driving for easy math.

 

[gimmie11s]

I did but due to a few reasons it is not 100%, at the speeds I was driving I was 4 mph off according to Waze

That will affect your mpg calculations big time. 4mph is a lot. Numbers in your original post as such, are NOT correct.




FWIW, I installed 35's on my DRW HO 4.10 truck and im now lucky to get 14 combined city/hwy driving.

Prior to the lift/tires, it would do 16-17 pretty easily.

 

[UglyViking]

In the nearly 15K miles I've put on my 2022 I've averaged 8.2% error on the EVIC, but as high as 22.6% (3.7 mpg optimistic) and as low as -.06% (.2 mpg pessimistic). The 8.2% error translates to ~1.1 mpg optimistic as an average. I subtract 10% while driving for easy math.

Perhaps I don't pay close enough attention, but the time I spent hand calcing and comparing, I found it pretty darn accurate. To me, anything around .5mpg is fine, so I guess maybe I just don't care enough?

End of the day, I'm driving a 9,000lb truck around that I've stupidly put huge tires on, so anything above 16mpg is pure win.